Method for dicing a substrate with back metal

ABSTRACT

The present invention provides a method for dicing a substrate with back metal, the method comprising the following steps. The substrate is provided with a first surface and a second surface wherein the second surface is opposed to the first surface. A mask layer is provided on the first surface of the substrate and a thin film layer is provided on the second surface of the substrate. The first surface of the substrate is diced through the mask layer to expose the thin film layer on the second surface of the substrate. A fluid from a fluid jet is applied to the thin film layer on the second surface of the substrate after the thin film layer has been exposed by the dicing step.

CROSS REFERENCES TO RELATED APPLICATIONS

This utility patent application is a divisional of commonly owned U.S.Utility patent application Ser. No. 14/034,164 entitled: Method forDicing a Substrate with Back Metal which was filed based on commonlyowned U.S. Provisional Patent Application Ser. No. 61/707,464 filed Sep.28, 2012, entitled: Method for Dicing a Substrate with Back Metal, theprior Utility Patent Application and Provisional Patent Applicationincorporated by reference herein.

BACKGROUND OF THE INVENTION Field of the Invention

The invention relates to semiconductor wafer processing and, moreparticularly, to a method and apparatus for dicing semiconductor waferinto a plurality of individual dice.

Description of the Related Art

Semiconductor die such as diodes, transistors and the like are commonlyprocessed (formed) simultaneously in a large area wafer. Such wafers maybe made of monocrystaline silicon or other materials, such as galliumnitride on a suitable substrate such as silicon or the like.

Plasma etching equipment is used extensively in the processing of thesesubstrates to produce semi-conductor devices. Such equipment typicallyincludes a vacuum chamber fitted with a high density plasma source suchas an Inductively Coupled Plasma (ICP) which is used to ensure high etchrates, necessary for cost-effective manufacturing. In order to removethe heat generated during the processing, the wafer (substrate) istypically clamped to a cooled support. A cooling gas (typically Helium)is maintained between the substrate and the support to provide a thermalconductance path for heat removal. A mechanical clamping mechanism, inwhich a downward force is applied to the top side of the substrate, maybe used, though this may cause contamination due to the contact betweenthe clamp and the substrate. More frequently an electrostatic chuck(ESC) is used to provide the clamping force.

After the processing steps are completed, the wafers are singulated,separating the die from the wafer. This “dicing,” separation orsingulating operation is commonly carried out by sawing through the“streets” between the die within the wafers. Singulating the die of thewafer, for example, by sawing the wafer along the streets after thewafer is complete, including metal layers on the back or front side, canbe a time consuming and costly process. Further, the singulation processcan damage portions of the die, including the sides of the die.

Because of the potential damage, additional spacing is required betweenthe dice on the wafer to prevent damage to the integrated circuits,e.g., the chips and cracks are maintained at a suitable distance fromthe actual integrated circuits so that the defects do not impair circuitperformance or reliability. As a result of the spacing requirements, notas many dice can be formed on a standard sized wafer and wafer area thatcould otherwise be used for circuitry is wasted. The use of a sawexacerbates the loss of real estate on a semiconductor wafer. The bladeof the saw is approximately fifteen microns thick. As such, to insurethat cracking and other damage surrounding the cut made by the saw doesnot harm the integrated circuits, approximately one to five hundredmicrons of separation is typically maintained between the circuitry ofeach of the dice. Furthermore, after cutting, the dice requiresubstantial cleaning to remove particles and other contaminants thatresult from the sawing process.

In an effort to overcome the disadvantages of sawing and scribing,chemical etching has been considered as an alternative for diesingulation. Two methods of separating die by chemical etching are wetetching and plasma etching. Wet chemical etching techniques require anetch mask to be formed on at least one side of the wafer and, in someembodiments, both sides of the wafer. The etch mask defines where thesubstrate will be etched and protects the integrated circuits from theetchant. Once the mask is in place, the wafer is to be immersed in a wetetchant such as potassium hydroxide in the case silicon substrates. Thewet etchant removes the substrate material from between the dice suchthat the dice are separated from one another. In the case of a siliconsubstrate, a wet etch technique is capable of removing silicon at a rateof about thirty microns per hour. Thus, even a wafer that has beenthinned to a thickness of about two hundred microns will require aboutseven hours to complete the dicing process. Furthermore, there arewell-known disadvantages to wet etch techniques such as the trenchesformed with a wet etch do not have substantially vertical sidewalls, thetrenches are relatively wide and, to achieve deep vertically directedtrenches, the semiconductor wafer can only have certain specific crystalorientations. Additionally, some materials, such as GaN, can bedifficult to wet etch with high enough rates to be economically feasiblein a manufacturing process. Therefore, there is a need in the art for amethod and apparatus for dicing a semiconductor wafer using a smallerseparation between the dice and a fast dicing process.

Recently plasma etching techniques have been proposed as a means ofseparating die and overcoming some of these limitations. After devicefabrication, the substrate is masked with a suitable mask material,leaving open areas between the die. The masked substrate is thenprocessed using a reactive-gas plasma which etches the substratematerial exposed between the die. The plasma etching of the substratemay proceed partially or completely through the substrate. In the caseof a partial plasma etch, the die are separated by a subsequent cleavingstep, leaving the individual die separated. The plasma etching techniqueoffers a number of benefits over mechanical dicing:

-   -   1) Breakage and chipping is reduced;    -   2) The kerf or street dimensions between die can be reduced to        well below twenty microns;    -   3) Processing time does not increase significantly as the number        of die increases;    -   4) Processing time is reduced for thinner wafers; and    -   5) Die topology is not limited to a rectilinear format.

For wafers that have back side metallization, die singulation is morecomplex. Back metal wafer dicing can be done with conventional sawingtechniques though lower saw speeds and more frequent blade changes arerequired. Back metal dicing represents a bigger challenge for plasmaetching techniques. Plasma etching systems are material dependent suchthat systems that are capable to etch through semiconductor materialslike silicon, gallium arsenide, and sapphire, are not typically capableof etching through metals or metal alloys—particularly metals typicallyused in back metal stacks (e.g., gold, silver, copper and nickel).Hence, a plasma system that can etch wafers for dicing is may not bewell suited to etch metals or metal alloys, thus a second etching toolmay be required. To add further complexity to back metal dry etching,plasma etching through metals typically has a very narrow process windowwith the complications of potential for sputtering of the etched metalonto the side of the newly singulated die which may ultimatelycompromise device performance or reliability. Furthermore, it may bepossible to etch the back metal prior to plasma etching the streetregions. While this approach would avoid metal byproduct re-depositionon the singulated die walls, it represents an additional etch step thatwould require an aligned mask patterns on the back of the wafer.

Nothing in the prior art provides the benefits attendant with thepresent invention.

Therefore, it is an object of the present invention to provide animprovement which overcomes the inadequacies of the prior art devicesand which is a significant contribution to the advancement to the dicingof semiconductor substrates using a plasma etching apparatus.

Another object of the present invention is to provide a method fordicing a substrate with back metal, the method comprising: providing thesubstrate having a first surface and a second surface, said secondsurface being opposed to said first surface, a mask layer on said firstsurface of the substrate, a thin film layer on said second surface ofthe substrate; dicing said first surface of the substrate through saidmask layer to expose said thin film layer on said second surface of thesubstrate; and applying a fluid from a fluid jet to said thin film layeron said second surface of the substrate after said thin film layer hasbeen exposed by the dicing step.

Yet another object of the present invention is to provide a method fordicing a substrate with back metal, the method comprising: providing aprocess chamber having a wall; providing a plasma source adjacent to thewall of the process chamber; providing a substrate support within theprocess chamber; providing the substrate having a first surface and asecond surface, said second surface being opposed to said first surface,a mask layer on said first surface of the substrate, a thin film layeron said second surface of the substrate; placing the substrate onto saidsubstrate support; generating a plasma using the plasma source; etchingsaid first surface of the substrate through said mask layer using thegenerated plasma, the etching step exposing said thin film layer on saidsecond surface of the substrate; and applying a fluid from a fluid jetto said thin film layer on said second surface of the substrate aftersaid thin film layer has been exposed by the etching step.

Still yet another object of the present invention is to provide a methodfor dicing a substrate, the method comprising: providing a processchamber having a wall; providing a plasma source adjacent to the wall ofthe process chamber; providing a work piece support within the processchamber; providing the substrate having a first surface and a secondsurface, said second surface being opposed to said first surface, a masklayer on said first surface of the substrate, and a thin film layer onsaid second surface of the substrate; placing a work piece onto saidwork piece support, said work piece having a support film, a frame andthe substrate; generating a plasma using the plasma source; etching saidfirst surface of the substrate through said mask layer using thegenerated plasma, the etching step exposing said thin film layer on saidsecond surface of the substrate; and applying a fluid from a fluid jetto said thin film layer on said second surface of the substrate aftersaid thin film layer has been exposed by the etching step.

The foregoing has outlined some of the pertinent objects of the presentinvention. These objects should be construed to be merely illustrativeof some of the more prominent features and applications of the intendedinvention. Many other beneficial results can be attained by applying thedisclosed invention in a different manner or modifying the inventionwithin the scope of the disclosure. Accordingly, other objects and afuller understanding of the invention may be had by referring to thesummary of the invention and the detailed description of the preferredembodiment in addition to the scope of the invention defined by theclaims taken in conjunction with the accompanying drawings.

SUMMARY OF THE INVENTION

The present invention describes a plasma processing apparatus whichallows for plasma dicing of a semiconductor substrate. After devicefabrication and wafer thinning, the front side (circuit side) of thesubstrate is masked using conventional masking techniques which protectsthe circuit components and leaves unprotected areas between the die. Thesubstrate is mounted on a thin tape which is supported within a rigidframe. The substrate/tape/frame assembly is transferred into a vacuumprocessing chamber and exposed to reactive gas plasma where theunprotected areas between the die are etched away. During this process,the frame and tape are protected from damage by the reactive gas plasma.After deep silicon etching of the substrate is accomplished using aplasma, a fluid jet is used to separate the back metal on the substrate.

Another feature of the present invention is to provide a method fordicing a substrate with back metal, the method comprising the followingsteps. The substrate is provided with a first surface and a secondsurface wherein the second surface is opposed to the first surface. Amask layer is provided on the first surface of the substrate and a thinfilm layer is provided on the second surface of the substrate. The thinfilm layer can further comprise a metal layer which can be approximatelyone to five microns thick. The first surface of the substrate is dicedthrough the mask layer to expose the thin film layer on the secondsurface of the substrate. A plasma deep silicon etch process can beemployed to accomplish the dicing. A fluid from a fluid jet is appliedto the thin film layer on the second surface of the substrate after thethin film layer has been exposed by the dicing step. The fluid from thefluid jet can be dispensed on an area on the substrate wherein the areais greater than a street width on the substrate. The fluid from thefluid jet can have a jet diameter wherein the jet diameter is greaterthan a die diameter on the substrate. The fluid jet can be pulsed duringthe application of the fluid to the thin film layer. The fluid from thefluid jet can be dispensed asymmetrically during the application of thefluid to the thin film layer. The fluid from the fluid jet can furthercomprise a liquid. The fluid from the fluid jet can further comprisewater. The fluid from the fluid jet can further comprise a solid. Thefluid from the fluid jet can further comprise a gas. The fluid from thefluid jet can further comprise a liquid. The fluid from the fluid jetcan further comprise a solid. The fluid jet can remove a portion of thethin film layer during the application of the fluid to the thin filmlayer. The etching step can leave a portion of the thin film layer. Theetching step can be selective to the thin film layer. The method canfurther comprise exposing the thin film layer from the first surface.

Yet another feature of the present invention is to provide a method fordicing a substrate with back metal, the method comprising the followingsteps. A process chamber having a wall is provide. A plasma sourceadjacent to the wall of the process chamber is provided. A substratesupport within the process chamber is provided. The substrate having afirst surface and a second surface is provided wherein the secondsurface is opposed to the first surface. A mask layer is provided on thefirst surface of the substrate. A thin film layer is provided on thesecond surface of the substrate. The substrate is placed onto thesubstrate support. A plasma is generated using the plasma source. Thefirst surface of the substrate is etched through the mask layer usingthe generated plasma. The etching step exposes the thin film layer onthe second surface of the substrate. A fluid from a fluid jet is appliedto the thin film layer on the second surface of the substrate after thethin film layer has been exposed by the etching step. The fluid jet canbe pulsed during the application of the fluid to the thin film layer.The fluid from the fluid jet can be dispensed asymmetrically during theapplication of the fluid to the thin film layer. The fluid from thefluid jet can further comprise a liquid. The etching step can leave aportion of the thin film layer. The etching step can be selective to thethin film layer. The method can further comprise exposing the thin filmlayer from the first surface.

Still yet another feature of the present invention is to provide amethod for dicing a substrate, the method comprising the followingsteps. A process chamber having a wall is provided. A plasma sourceadjacent to the wall of the process chamber is provided. A work piecesupport within the process chamber is provided. The substrate having afirst surface and a second surface is provided wherein the secondsurface is opposed to the first surface. A mask layer is provided on thefirst surface of the substrate and a thin film layer is provided on thesecond surface of the substrate. A work piece is placed onto the workpiece support wherein the work piece has a support film, a frame and thesubstrate. A plasma is generated using the plasma source. The firstsurface of the substrate is etched through the mask layer using thegenerated plasma. The etching step exposes the thin film layer on thesecond surface of the substrate. A fluid is applied from a fluid jet tothe thin film layer on the second surface of the substrate after thethin film layer has been exposed by the etching step. The fluid jet canbe pulsed during the application of the fluid to the thin film layer.The fluid from the fluid jet can be dispensed asymmetrically during theapplication of the fluid to the thin film layer. The fluid from thefluid jet can further comprise a liquid. The etching step can leave aportion of the thin film layer. The etching step can be selective to thethin film layer. The method can further comprise exposing the thin filmlayer from the first surface.

The foregoing has outlined rather broadly the more pertinent andimportant features of the present invention in order that the detaileddescription of the invention that follows may be better understood sothat the present contribution to the art can be more fully appreciated.Additional features of the invention will be described hereinafter whichform the subject of the claims of the invention. It should beappreciated by those skilled in the art that the conception and thespecific embodiment disclosed may be readily utilized as a basis formodifying or designing other structures for carrying out the samepurposes of the present invention. It should also be realized by thoseskilled in the art that such equivalent constructions do not depart fromthe spirit and scope of the invention as set forth in the appendedclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1a is a top down view of a semiconductor substrate illustratingindividual devices separated by streets on the front side of thesubstrate;

FIG. 1b is a top down view of a semiconductor substrate illustrating aback metal layer on the back side of the substrate;

FIG. 2a is a cross-sectional view of a semiconductor substrate with backmetal illustrating individual devices separated by streets;

FIG. 2b is a cross-sectional view of a semiconductor substrate with backmetal illustrating individual devices separated by streets with thesubstrate being etched through to the back metal layer;

FIG. 3a is a cross-sectional view of a fluid jet being applied to backmetal on a semiconductor wherein the semiconductor substrate has beenpreviously diced according to an embodiment of the present invention;

FIG. 3b is a cross-sectional view of a fluid jet being applied to backmetal on a semiconductor wherein the semiconductor substrate has beenpreviously diced according to an embodiment of the present invention;and

FIG. 4 is a flow chart of a method to a fluid jet to back metal of aplasma diced substrate to finalize the singulation of the die.

Similar reference characters refer to similar parts throughout theseveral views of the drawings.

DETAILED DESCRIPTION OF THE INVENTION

A method of singulating the die of the wafer will now be described.Silicon devices are typically fabricated on silicon wafers. Many die aretypically present on one wafer. These die can be various sizes andshapes. It is possible to have different die types within the samewafer. In order to make a useful device, the individual die must beseparated from the wafers. In order to accomplish this, non-functionalareas of the wafer are purposely left between the devices. These areasare known as street regions or kerfs. These street regions are typicallyremoved during the die singulation process. This material removal can beaccomplished in a number of ways including sawing, laser cutting(stealth and ablation) and plasma etching.

A common practice in semiconductor device production is to coat the backof the wafer with a metal alloy, usually made up but not limited toaluminum, silver, gold, copper, nickel, and/or titanium. The purpose ofthe back metal is to provide a conductive layer for soldering die to dieand/or a package in order to create a product. This coating is typicallydone via plasma vapor deposition, sputtering and/or e-beam evaporation.The back metal plating step is usually done prior to any micromachining. Typical back metal thicknesses are usually between one to tenmicrons.

As shown in FIG. 1a , a semiconductor substrate (wafer) 110 withindividual devices 120 separated by streets 125 on the front side of thesubstrate 110. The wafer 110 can be of any desired material, such assilicon, gallium arsenide, silicon carbide and the like. Any number ofseparate devices 120 can be provided as part of the wafer 110. Once thefront side circuitry has been completed, the substrate 110 may bethinned prior to back metal deposition on the substrate. FIG. 1b showsthe semiconductor substrate 110 with a back metal layer 130 on the backside of the substrate 110.

A mask layer is deposited along the first side (front side) of the waferand a portion of the mask is removed to leave mask deposits, thusexposing the top of the wafer as an etch window. An adhesive layer ofthe type that can be dissolved or whose adhesive effect can beneutralized, for example by radiation or by chemical means, may be usedto adhere a carrier layer to the top surface of the wafer. The carrierlayer may be a rigid plate that secures together the die of the waferwhile the grinding or polishing step at the other surface of the waferis performed. With the wafer physically supported or reinforced by thecarrier layer, the second side or the bottom or rear surface of thewafer is ground back and polished to a plane. With the carrier layerstill in place and securing or reinforcing the wafer, a back metal orthe like may be deposited on the bottom surface of the wafer.

The back metal deposition is typically deposited on the second (back)side of the wafer—opposite the front side circuitry. There are manyprocess flows known in the art to fabricate a thinned substrate withcircuitry with back metal. The order of circuit fabrication, thinning,and metallization steps may vary depending on the specifics of thedevice application and substrate fabrication strategy.

Once the front side circuitry has been fabricated and the back metaldeposition completed, the substrate is ready for wafer dicing (diesingulation). Typically, the substrate is supported during the dicingoperation. This support can be in the form of a rigid carrier or aflexible membrane (e.g., dicing tape) supported by a rigid frame (e.g.,dicing frame) as is known in the art. This singulation may beaccomplished through mechanical means including sawing and breaking,optical means including laser ablation and stealth dicing, or chemicalmeans including plasma dicing. A recent method of high rate plasmadicing, which has been developed by Plasma Therm LLC, can now completelyetch through wafers 110 mounted on dicing tape as shown in FIG. 2a .This high rate plasma dicing, known as micro dice singulation (MDS), isa fast-switching deep silicon etch process. The result is a diesingulation method that maintains smooth kerf edges, with the additionalbenefits of narrower kerf s, control of the wall angle, and a higherthroughput. Once the die are singulated, the dicing tape is expanded forthe pick and place tools just the same as any current methods of diesingulation that are known in the art. To assimilate the plasma dicingprocess into semiconductor production, the wafers are diced on industrystandard wafer frames and wafer tape. While the plasma dicing operationbeneficially removes the substrate material between the die, it can bedifficult for the plasma to remove the remaining backside metallization130 connecting the die as shown in FIG. 2 b.

The following describes the method to selectively remove the one to tenmicrons thick back metal layer 130 remaining after a deep silicon etchplasma dicing of a patterned silicon wafer 110 less than or equal toapproximately two hundred fifty microns thick in order to complete thedie singulation process while still being able to integrate into thestandard back-end semiconductor packaging system such as pick and place.In order for the method to be successful, the back metal 130 must remainon each die and be compatible with downstream operations, while themetal between the die must be separated and/or removed.

The key to separating and/or removing the back metal 130 after theplasma dicing process is to feed a flowing fluid 320 from a fluid jet340 at a given pressure over a mounted wafer 110 for a specified time asshown in FIGS. 3a and 3b . Specifically, once the mounted wafer 110 isremoved from the plasma dicing tool, it is flipped onto a new wafer tapeand frame so that the die are adhered and the back metal 130 exposed.The fluid 320 is then dispensed from the fluid jet 340 onto the exposedback metal 130 with a pressure large enough to clear the kerfs away, butnot strong enough to knock the die from the wafer tape. When all thekerfs are clear of the back metal 130, the wafer 110 is ready to beexpanded and then the diced packaged. The controlled variables for thissolution are the fluid type, pressure/flow rate of the fluid, flowpattern, height to sample, flow angle, feed pattern relative to kerfpattern, feed rate, temperature of the fluid or sample, and exposuretime.

The example above describes a process where the plasma diced wafer isinverted and reattached to dicing tape such that the back metal side ofthe wafer is exposed. A general flow diagram of the process according toone embodiment of the present invention is shown in FIG. 4. It isimportant to note that it is possible to practice the invention in anumber of different hardware configurations. In an alternate embodiment,the wafer could remain on the tape carrier post plasma etch with thefluid being applied to the thin film in the street regions of thesubstrate from the through openings in the first surface of thesubstrate. In this configuration, it is preferred that the substratesupport be compliant (e.g., non rigid).

In yet another configuration, after the dicing process has removed asubstantial amount of the substrate material, the wafer can be mountedand held to a substrate support. The substrate support can be rigid. Thesubstrate can be held to the support using a number of methods includingpressure based (vacuum), adhesive, or electrostatic means. The substratecan be mounted with second side of the substrate being exposed to thefluid jet.

The process most likely will require a flip of the wafer after the deepsilicon etch process and then placed on a tool that passes the fluidover the back metal. Once the back metal has been selectively separatedand/or removed, the singulated die can then be expanded and sent into adownstream packaging work flow.

At least one device is fabricated on a wafer where the wafer containsdevice regions and street regions. There can be lots of device types ofsemiconductor devices such as Integrated circuits (ICs),Micro-Electro-Mechanical-Systems (MEMS) devices, Optical devices, etc.The wafer types to support different device types can be Semiconductor(e.g., Si, Ge, etc.); Compound Semiconductor (e.g., GaAs, InP, GaN, SiC,etc.); Insulating (e.g., Quartz, Pyrex, etc.); or Conducting (e.g.,metal, etc.).

The street regions are removed or broken to allow separation ofindividual die. The separated die will become a functioning device orpart of a larger device which are packaged as individual device orintegrated with other die to form lager device.

A substrate with a second surface (front) opposed to a first surface(back) with a thin film on the second surface. The thin film can be acomposite stack, could contain metal (e.g., Au, Ag, Al, or Cu). Thecoverage of the thin film on the second surface of the substratecorresponds to a portion of the street area on the first surface (e.g.,the thin film on the second surface of the substrate has some degree ofoverlap with the street regions as defined on the front (first) surfaceof the substrate). The thin film can be less than approximately twentymicrons thick, preferably one to five microns thick. The etch process toremove material from the street region of the wafer from the first sidecan be chemical etching (e.g., plasma etching using the Bosch process).Alternately, the etch process to remove material from the street regioncan be through the use of a laser. Plasma etching can result in slopedfeatures, vertical features or features with a retrograde (e.g.,undercut) profile. The chemical etching process can contain a halogencontaining etchant. The etch process can be selective to the thin filmwith a thin film: substrate selectivity >10:1; a selectivity >100:1 or1000:1. Etch selectivity can be a ratio of the film etch rate to thesubstrate etch rate. The substrate removal process leaves at least aportion of the thin film overlapping the street region. The etchingprocess can expose a portion of the thin film from the first surface ofthe substrate. The thin film substantially can be unsupported by thesubstrate in at least some portion or all of the street regions.

The substrate can be held on a substrate support. The substrate supportcan contain an adhesive such as dicing tape. The substrate support canhave an electrostatic chuck and/or a vacuum chuck. The substrate supportis in contact with the first side of the substrate (front). A fluiddispensed from a fluid jet is applied to a portion of the thin filmwhere the fluid pressure of the dispensed fluid from the fluid jet canbe greater than the thin film ultimate tensile strength. The fluidpressure of the dispensed fluid from the fluid jet can be less than thethin film to substrate adhesion strength.

The wafer could be die side up or die side down when it is being exposedto the dispensed fluid from the fluid jet. Wafers exit the micro dicesingulation tool die side up. Die side down may require the substrate tobe inverted between the removal of the substrate material in the streetand application of the fluid jet to the thin film.

The fluid from the fluid jet imparts a force onto the thin film thatwill damage or remove the film. The type of dispensed fluid from thefluid jet could be Compressed Air, Nitrogen, Argon, or Deionized Water.The fluid pressure of the dispensed fluid from the fluid jet can begreater than the ultimate tensile strength of the kerf. The ultimatetensile strength of the thin film is based on the material composition,the kerf width, and thickness of the thin film (e.g., back metal). Ifthe pressure of the dispensed fluid from the fluid jet is too great,then the fluid jet may damage the singulated device. This damage maycome in the form of removing the singulated die from the substratesupport (e.g., dicing tape). Alternatively, the damage may come in theform of removing portions of the thin film from the final device. Theflow pattern of the fluid of the dispensed fluid from the fluid jet canbe chosen from a wide range of geometries including: straightcylindrical, flat fan, cone, or square which is dependent on the fluidnozzle on the fluid jet. The height that the fluid is expressed from thenozzle of the fluid jet relative to the wafer directly increases ordecreases the pressure of the fluid that is applied to the wafer.Typically the fluid jet is expressed less than 25 cm from the wafersurface. In a preferred embodiment, the fluid jet is expressed at aheight less than 3 cm from the wafer surface. In fluid jetconfigurations where the spray pattern is diverging, the height that thefluid is expressed from the nozzle of the fluid jet relative to thewafer also adjusts the amount of surface area on the wafer that will beaffected by the expressed fluid from an individual fluid jet. A balancebetween pressure and exposure of the dispensed fluid from the fluid jetis necessary for efficiently separating back metal on the substrate.

The fluid jet can express the fluid at a nearly mono-disperse angle(e.g., near unidirectional stream) or in a pattern that contains adistribution of fluid velocities and directions (e.g., a conical or fanshaped nozzle). The nozzle of the fluid jet can be tilted so that theflow of fluid from the fluid jet can be optimized for kerf clearing onthe substrate. The feed rate of the fluid flow pattern from the fluidjet over the wafer can be optimized for kerf clearing on the substrate.The fluid dispensed from the fluid jet can be optimized for temperatureof the fluid and the exposure time of the back metal to the fluid foroptimized kerf clearing on the substrate.

The fluid dispensed from the fluid jet is applied to the thin film. Inone embodiment, the fluid is dispensed to the second surface of thesubstrate. In applying the fluid dispensed from the fluid jet to thesecond surface, the dispensed fluid jet dimension can be:

-   -   1. greater than the street width on the substrate;    -   2. greater than one die dimension on the substrate;    -   3. covering a portion of at least one die on the substrate; or    -   4. less than the dimension of the substrate.

In applying the fluid dispensed from the fluid jet to the second surfaceof the substrate, the substrate can be moved relative to the fluid jet.The fluid jet can be moved relative to the substrate and the movementmay be coplanar or non-coplanar. The fluid jet and the substrate canboth be moved relative to one another during the application of thefluid dispensed from the fluid jet to the substrate.

In applying the fluid dispensed from the fluid jet to the surface of thesubstrate, the fluid dispensed from the fluid jet can be discontinuousand/or pulsed. The pulsing of the fluid dispensed from the fluid jet canbe varied based on jet pressure and/or flow rate of the fluid dispensedfrom the fluid jet.

In applying the fluid dispensed from the fluid jet to the second surfaceof the substrate, the fluid dispensed from the fluid jet can be shaped:

-   -   1. symmetric in at least one dimension;    -   2. conical—hollow and/or solid cone    -   3. fan shaped;    -   4. asymmetric in at least one dimension; or    -   5. a curtain, which can be a linear curtain.

The fluid jet can be comprised of multiple individual fluid jets. Thefluid jet can be comprised of an array of jets that can be arranged as alinear array. The array can be a two dimensional array that can beregularly or irregularly spaced. The area of the array of jets can belarger or smaller than the substrate area. The array of jets can bemoved relative to the substrate, moved linearly and/or rotationally. Thesubstrate may be moved relative to the array of jets, moved linearlyand/or rotationally.

In applying the fluid dispensed from the fluid jet to the second surfaceof the substrate, the fluid dispensed from the fluid jet may impact thesecond surface of the substrate at a near normal incidence or at anotherprescribed angle of incidence. The dispensed fluid from the fluid jetmay be substantially unidirectional. In applying the fluid dispensedfrom the fluid jet to the second surface of the substrate, the fluiddispensed from the fluid jet may impact the substrate at a plurality ofangles. The angle that the fluid is dispensed from the fluid jet to thesecond surface of the substrate may be adjustable. The angle that fluidis dispensed from the fluid jet to the second surface of the substratemay be moveable relative to the surface of the substrate. The substratemay be moveable relative to the fluid nozzle of the fluid jet. Both thesubstrate and the fluid nozzle of the fluid jet may be movable relativeto each other. The angle that the fluid is dispensed from the fluid jetto the second surface of the substrate may be variable over time.

In one embodiment where the fluid jet impinges on areas of the waferwhere the thin film has been separated, it is preferred that the angleof fluid impinging on the separated die is less than approximately 45degrees from normal incidence. This limitation in angle reduces thelikelihood that the pressure from the fluid jet will cause the separateddie to be removed from the substrate support during the fluid jetoperation (e.g., at off normal angles, the fluid jet may cause thesingulated die to lose adhesion to the dicing tape and be lost).

The height at which fluid is dispensed from the nozzle of the fluid jetrelative to the surface of the substrate may be adjustable. The heightat which fluid is dispensed from the nozzle of the fluid jet relative tothe surface of the wafer can be held constant during the thin filmsingulation process. The height at which fluid is dispensed from thenozzle of the fluid jet relative to the surface of the wafer can bevaried during the back metal process.

The temperature of the fluid dispensed from the fluid jet can becontrolled. The fluid dispensed from the fluid jet can contain a liquid(e.g., water), a solid and/or gas (e.g., nitrogen). The fluid dispensedfrom the fluid jet can contain droplets. The droplets can be less thanapproximately one mm in diameter. The droplets can be less than onehundred microns in diameter. The fluid dispensed from the fluid jet cancontain gas bubbles in a liquid. The fluid dispensed from the fluid jetcan contain immiscible liquids, surfactants and/or anti-corrosionadditives. The fluid dispensed from the fluid jet can be an aerosol.

The fluid jet energy flux as dispensed from the fluid jet can besufficient to damage the thin film. The fluid jet energy flux asdispensed from the fluid jet can remove a portion of the thin film. Thefluid jet energy flux as dispensed from the fluid jet can damage aportion of the thin film.

The thin film separation width may be defined by the dicing width on thesubstrate. The film separation dimension on the substrate is less thanthe street region. The film separation dimension on the substrate may beequal to the street region. Minimal film separation or damage in the dieregion can occur or no film separation in the die region can occur. Anyfilm damage that may occur in the die region does not impair deviceperformance.

It is important to note that while the method above describes the fluidjet technique in conjunction with plasma etch singulation, the fluid jetmethod is compatible with all singulation techniques that removesubstantially all the wafer material leaving a thin film connecting thedie. The method is particularly relevant for use with dicing techniquesthat leave a thin film substantially unsupported by the substratebetween the die.

The present disclosure includes that contained in the appended claims,as well as that of the foregoing description. Although this inventionhas been described in its preferred form with a certain degree ofparticularity, it is understood that the present disclosure of thepreferred form has been made only by way of example and that numerouschanges in the details of construction and the combination andarrangement of parts may be resorted to without departing from thespirit and scope of the invention.

Now that the invention has been described,

What is claimed is:
 1. A method for dicing a substrate with back metal,the method comprising: providing a substrate support having anelectrostatic chuck; providing the substrate having a first surface anda second surface, said second surface being opposite to said firstsurface, a mask layer on said first surface of the substrate, the backmetal layer on said second surface of the substrate; dicing said firstsurface of the substrate through said mask layer to expose the backmetal layer on said second surface of the substrate; electrostaticallyclamping the substrate to the electrostatic chuck; and damaging aportion of the back metal layer by applying a fluid from a fluid jet tothe back metal layer on said second surface of the substrate after theback metal layer has been exposed by the dicing step, said fluid fromsaid fluid jet being applied to the substrate while the substrate iselectrostatically clamped to the electrostatic chuck.
 2. The methodaccording to claim 1 wherein the back metal layer being approximatelyone to five microns thick.
 3. The method according to claim 1 whereinsaid fluid from said fluid jet being dispensed at an angle less than 45degrees from normal incidence to the back metal layer of the substrate.4. The method according to claim 1 further comprising controlling thetemperature of said fluid from said fluid jet.
 5. The method accordingto claim 1 wherein said fluid jet being pulsed during the application ofsaid fluid to the back metal layer.
 6. The method according to claim 1wherein said fluid from said fluid jet being dispensed in a fan shapeduring the application of said fluid to the back metal layer.
 7. Themethod according to claim 1 wherein said fluid from said fluid jet beingdispensed at a fluid jet area, said fluid jet area being larger than asubstrate area.
 8. The method according to claim 1 wherein said fluidfrom said fluid jet being dispensed at a fluid jet area, said fluid jetarea being smaller than a substrate area.
 9. The method according toclaim 1 further comprising moving said fluid jet relative to thesubstrate.
 10. The method according to claim 9 further comprising movingthe substrate relative to said fluid jet.
 11. The method according toclaim 1 further comprising applying the fluid from said fluid jetsymmetrically in at least one direction.
 12. The method according toclaim 1 further comprising applying the fluid from said fluid jetasymmetrically in at least one direction.
 13. The method according toclaim 1 further comprising exposing the back metal layer from said firstsurface.